PURPOSE: To enhance the steering efficiency by providing a duct at the outlet from a nozzle of a water jet propulsive machine in such a way as capable of swinging the head to the left and right, furnishing a main jet at the tail of this duct, furnishing aux. jets in the left and right side walls of the duct, and installing a rotatable guide plate at each aux. jet.

CONSTITUTION: In a water jet propulsive machine, the water taken in from a water intake 22 furnished at the bottom of a vessel 21 through rotation of a pump impeller 25 in a pump casing 23 caused by an engine is baffled by a diffuser 26 and jetted out of a nozzle 27, and a duct 32 capable of swinging its head to the left and right with a pin 31 as fulcrum is provided at the tail of this nozzle 27. A main jet 33 is provided at the tail of this duct 32 while aux. jets 34, 35 are provided in the left and right side walls. At these aux. jets 34, 35, guide plated 38, 39 rotatable round vertical rotary shafts, 36, 37 are installed in their positions on the inner side wall of the duct 32, respectively, and rotated through pins 42, 43 interlocked with the head swinging motion of the duct 32.